长期施用尿素降低赤红壤旱地耕层pH的特征与预测

【目的】阐明长期不同施肥处理的赤红壤旱地耕层土壤pH变化特征，并以模型预测土壤pH的未来变化，为区域土壤高产稳产和可持续利用提供理论依据。【方法】在闽东南赤红壤旱地花生–甘薯轮作制连续进行16年化肥定位试验和14年化肥配施有机肥定位试验，测定各施肥处理的历年耕层土壤pH。以实测土壤pH为依据构建灰色预测模型，并进行模型可靠性验证。【结果】连续16年实测结果表明，不施肥CK处理和不施氮肥(尿素)处理(RF-N)的耕层土壤pH在16年间从基础土壤的5.90分别提高到6.24±0.18和6.21±0.17，分别年均递增0.021和0.019个pH单位；习惯施肥(FP)、推荐施肥(RF)、不施磷肥(RF-P)和不施钾肥(RF-K)处理均导致土壤酸化，且酸化程度没有显著差异。化肥配施有机肥可抑制土壤酸化或提高土壤pH。连续14年推荐施肥配施猪粪(RF+PM)处理的土壤pH从基础土壤的5.73提高到5.80±0.36，显著高于RF和推荐施肥配施商品有机肥(RF+COM)两个处理，年均递增0.005个pH单位，但与推荐施肥配施稻草(RF+S)处理的差异不显著；RF+COM处理抑制土壤酸化的效果较差，...

Characteristics and prediction of topsoil acidification of latosolic red soil caused by long-term urea application

  【Objectives】  Studying the effects of long-term fertilization on the dynamics of the topsoil pH and predicting soil pH trend are important to provide optimal nutrient management for soil fertility improvement and stable high yield.  【Methods】  Two different experiments involving application of chemical fertilizer or combined application of chemical and organic fertilizers were carried out in latosolic red soil of southeast Fujian for 16 years and 14 years, respectively, and annual soil pH were tested. Soil pH grey prediction model was set up to explore the difference in soil pH and dynamics among treatments.  【Results】  The main factor responsible for soil acidification was chemical nitrogen fertilizer (urea) application in latosolic red soil. The tested data for sixteen years showed that topsoil pH in CK (no fertilizer) and RF?N (without N in the recommended fertilizer) treatments increased to 6.24±0.18 and 6.21±0.17 from 5.90 of basal soil, respectively, with an annual average increment of 0.021 and 0.019, respectively. Soil acidification was observed in FP (farmer’s practice), RF (recommended fertilizer), without P in RF (RF?P) and without K in RF (RF?K). Even though, there was no significant difference in acidification level. Chemical fertilizers combined application with organic fertilizers inhibited soil acidification. The soil pH in RF+PM (recommended fertilizers and pig manure combination experiment for fourteen years) increased from 5.73 of basal soil to 5.80±0.36, which was significantly higher than that of RF and RF+COM (recommended fertilizers combined with commercial manure combination experiment) with an annual increase of 0.005. However, there was no significant difference between RF+PM and RF+S (recommended fertilizers combined with rice straw). RF+COM had a limited influence on inhibiting soil acidification, as soil pH declined at rate of 0.019 unit/a, which was not significantly different from RF treatment. The grey prediction simulation models of soil pH showed the fitting errors ranged from 0.997% to 4.321% among fertilization treatments; the soil pH change had obvious periodical characteristics, and the inflection point appeared in the third or fourth years of the experiment; soil pH trend was significantly affected by fertilization. Soil pH in CK and RF?N was going up in the first 3 years, and then stabilized at about 6.20 after that. Soil pH declined in the treatments of FP, RF, RF?P, RF+COM, RF+PM, and RF+S, respectively in the third and fourth year. Soil pH in the treatments of FP, RF, RF?P and RF+COM stabilized at about 5.50 in the first 3 or 4 years, but soil pH in RF+PM and RF+S was going up, and reached 6.26 and 5.91 in the 14th year, respectively, which were 0.53 and 0.18 units higher than that of the basal soil, respectively.   【Conclusion】  The main reason that led to soil acidification was long-term application of recommended nitrogen or higher nitrogen fertilizer (urea) in the latosolic red soil. The soil pH change had obvious periodical characteristics, and the inflection point appeared at the third the fourth years after the long-term experiments. The treatments in which1/3 of the N input was provided by decomposed pig manure or rice straw on the basis of recommended fertilization significantly increased soil pH after the inflection point, the effect was as follows: decomposed pig manure > rice straw.